Chapter 1
Brownian Ratchets and Molecular
Motors
Molecular motors are biological molecular machines that are the essential agents of
movement in living organisms. In general terms, a motor is a device that consumes
energy in one form and converts it into motion or mechanical work; for example,
many protein-based molecular motors harness the chemical free energy released
by the hydrolysis of ATP in order to perform mechanical work. One important
difference between molecular motors and macroscopic motors is that molecular
motors operate in the thermal bath, an environment in which the fluctuations due to
thermal noise are significant. Wikipedia [1], their action are often described in terms
of Brownian Ratchet (BR) and Power Stroke (PS), in other words Brownian ratchet
and Power Stroke are models of molecular motors [2]. For an excellent synthesis on
molecular motor see [3].
1.1 The Force-Generation
1.1.1 Maximum Driving Force
The hydrolysis of one ATP molecule releases free energy 0 of about 0.50×10 −19
J [corresponding to 7.3 Kcal/M or 12k B T at typical in vitro temperatures, T [4]]. If
all of this free energy could be converted into mechanical energy and move the
motor protein through a distance = d, the step size, the force exerted would be
f max = 0 /d
(1.1)
Considering that one molecule of ATP is sufficient to translocate the motor protein
by one step [6], this expression clearly represents the maximal driving force that can
be exerted. For a kinesin moving on a microtubule with d = 8.2 nm [5–7] it yields
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
J. A. Fornés, Principles of Brownian and Molecular Motors, Springer Series in
Biophysics 21, https://doi.org/10.1007/978-3-030-64957-9_1
1
Brownian Ratchets and Molecular
Motors
Molecular motors are biological molecular machines that are the essential agents of
movement in living organisms. In general terms, a motor is a device that consumes
energy in one form and converts it into motion or mechanical work; for example,
many protein-based molecular motors harness the chemical free energy released
by the hydrolysis of ATP in order to perform mechanical work. One important
difference between molecular motors and macroscopic motors is that molecular
motors operate in the thermal bath, an environment in which the fluctuations due to
thermal noise are significant. Wikipedia [1], their action are often described in terms
of Brownian Ratchet (BR) and Power Stroke (PS), in other words Brownian ratchet
and Power Stroke are models of molecular motors [2]. For an excellent synthesis on
molecular motor see [3].
1.1 The Force-Generation
1.1.1 Maximum Driving Force
The hydrolysis of one ATP molecule releases free energy 0 of about 0.50×10 −19
J [corresponding to 7.3 Kcal/M or 12k B T at typical in vitro temperatures, T [4]]. If
all of this free energy could be converted into mechanical energy and move the
motor protein through a distance = d, the step size, the force exerted would be
f max = 0 /d
(1.1)
Considering that one molecule of ATP is sufficient to translocate the motor protein
by one step [6], this expression clearly represents the maximal driving force that can
be exerted. For a kinesin moving on a microtubule with d = 8.2 nm [5–7] it yields
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
J. A. Fornés, Principles of Brownian and Molecular Motors, Springer Series in
Biophysics 21, https://doi.org/10.1007/978-3-030-64957-9_1
1